📡Systems Approach to Computer Networks Unit 1 – Computer Networks and Internet Basics

Key Concepts and Terminology

• Computer networks enable communication and resource sharing between devices (computers, servers, printers) connected via communication channels
• Protocols define the rules and conventions for data transmission between network devices
• Bandwidth measures the maximum amount of data that can be transmitted over a network connection per unit of time (bps, Kbps, Mbps)
• Latency refers to the delay or time required for data to travel from its source to its destination across a network
  • Factors affecting latency include propagation delay, transmission delay, queuing delay, and processing delay
• Throughput represents the actual amount of data successfully transferred over a network per unit of time
• Network topology describes the physical or logical arrangement of devices, nodes, and connections in a network (bus, star, ring, mesh)
• IP addresses uniquely identify devices on a network and enable data routing between them
  • IPv4 uses 32-bit addresses, while IPv6 uses 128-bit addresses to accommodate more devices

Network Architecture and Models

• Network architecture defines the overall structure, components, and principles of a network's design and operation
• The OSI (Open Systems Interconnection) model is a conceptual framework that divides network communication into seven layers
  1. Physical layer: Deals with the physical transmission of raw data bits over a communication channel
  2. Data link layer: Provides reliable data transfer between adjacent network nodes and handles error detection and correction
  3. Network layer: Responsible for routing data packets between source and destination nodes across multiple networks
  4. Transport layer: Ensures reliable, error-free, and ordered delivery of data segments between end-to-end applications
  5. Session layer: Establishes, manages, and terminates connections between applications
  6. Presentation layer: Handles data formatting, encryption, and compression for application-specific needs
  7. Application layer: Provides services directly to end-user applications (HTTP, FTP, SMTP)
• The TCP/IP model is a simplified, four-layer model used in the Internet protocol suite
  1. Link layer: Combines the physical and data link layers of the OSI model
  2. Internet layer: Equivalent to the network layer in the OSI model, responsible for IP addressing and routing
  3. Transport layer: Provides end-to-end communication services, similar to the OSI transport layer
  4. Application layer: Includes the session, presentation, and application layers of the OSI model

Types of Networks and Topologies

• Local Area Networks (LANs) connect devices within a limited geographic area (office, building, campus)
  • LANs typically use Ethernet or Wi-Fi technologies for high-speed, low-latency communication
• Wide Area Networks (WANs) connect geographically dispersed LANs, enabling communication across large distances
  • WANs often use leased lines, satellite links, or the Internet for long-distance connectivity
• Wireless Local Area Networks (WLANs) use radio waves to connect devices without the need for physical cables
  • Wi-Fi is the most common WLAN technology, based on the IEEE 802.11 standards
• Bus topology connects all devices to a single cable or backbone, with each device having a unique identifier
• Star topology connects all devices to a central hub or switch, providing a single point of failure but easier management
• Ring topology connects devices in a closed loop, with each device acting as a repeater to pass data along the ring
• Mesh topology connects each device to multiple other devices, providing redundancy and fault tolerance but higher complexity

Internet Protocols and Standards

• TCP (Transmission Control Protocol) provides reliable, connection-oriented, and error-checked delivery of data segments
  • TCP establishes a virtual connection between sender and receiver, ensuring data is delivered in the correct order
• UDP (User Datagram Protocol) offers a connectionless, unreliable, and best-effort delivery of data packets
  • UDP is faster than TCP but does not guarantee packet delivery or ordering, suitable for real-time applications (VoIP, streaming)
• HTTP (Hypertext Transfer Protocol) is an application-layer protocol for transmitting web pages and other content over the Internet
• FTP (File Transfer Protocol) enables the transfer of files between a client and a server over a network
• SMTP (Simple Mail Transfer Protocol) is used for sending and relaying email messages between mail servers
• DNS (Domain Name System) translates human-readable domain names (www.example.com) into IP addresses
• DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses and other network configuration parameters to devices

Network Devices and Hardware

• Routers connect multiple networks and forward data packets between them based on IP addresses
  • Routers use routing tables and protocols (RIP, OSPF, BGP) to determine the best path for data transmission
• Switches connect devices within a network and forward data frames based on MAC addresses
  • Switches maintain a MAC address table to efficiently direct traffic between connected devices
• Hubs are simple devices that repeat incoming data to all connected ports, causing collisions and reduced efficiency
• Modems (modulators-demodulators) convert digital signals to analog signals and vice versa for transmission over telephone lines
• Network Interface Cards (NICs) are hardware components that connect a device to a network and have unique MAC addresses
• Wireless Access Points (WAPs) allow wireless devices to connect to a wired network, acting as a central hub for WLANs
• Firewalls monitor and control incoming and outgoing network traffic based on predetermined security rules

Data Transmission and Encoding

• Data is transmitted over networks in the form of bits (binary digits), which are electrical or optical pulses representing 0s and 1s
• Encoding schemes convert data into a format suitable for transmission over a specific medium (copper wire, fiber optic cable, radio waves)
  • Manchester encoding represents each bit by a transition (low to high or high to low) in the middle of the bit period
  • Non-Return-to-Zero (NRZ) encoding maintains a constant voltage level for the duration of each bit (high for 1, low for 0)
• Modulation techniques modify a carrier signal to encode digital information for transmission over analog channels
  • Amplitude Shift Keying (ASK) varies the amplitude of the carrier signal to represent digital data
  • Frequency Shift Keying (FSK) changes the frequency of the carrier signal to represent digital data
  • Phase Shift Keying (PSK) alters the phase of the carrier signal to represent digital data
• Multiplexing allows multiple signals to share a single communication channel, increasing efficiency and capacity
  • Time Division Multiplexing (TDM) allocates time slots to each signal, transmitting them in a fixed sequence
  • Frequency Division Multiplexing (FDM) assigns a different frequency band to each signal, transmitting them simultaneously

Network Security and Privacy

• Confidentiality ensures that data is accessible only to authorized parties, preventing unauthorized disclosure
  • Encryption algorithms (AES, RSA) convert plaintext into ciphertext, making it unreadable without the decryption key
• Integrity guarantees that data has not been altered or tampered with during transmission or storage
  • Hash functions (MD5, SHA) generate a fixed-size digest of the data, which can be used to verify its integrity
• Availability ensures that network resources and services are accessible to authorized users when needed
  • Redundancy, load balancing, and backup systems help maintain high availability and minimize downtime
• Authentication verifies the identity of users or devices before granting access to network resources
  • Passwords, biometric data, and digital certificates are common authentication methods
• Access control restricts access to network resources based on user roles, permissions, and policies
  • Access control lists (ACLs) define which users or groups can access specific resources and actions
• Virtual Private Networks (VPNs) create secure, encrypted connections over public networks, enabling remote access and privacy
• Intrusion Detection Systems (IDS) and Intrusion Prevention Systems (IPS) monitor network traffic for suspicious activities and threats

Practical Applications and Real-World Examples

• Voice over IP (VoIP) enables voice communication over IP networks, replacing traditional telephone systems (Skype, Zoom)
• Internet of Things (IoT) connects everyday devices (smart home appliances, wearables) to the Internet for remote monitoring and control
• Cloud computing relies on network infrastructure to provide scalable, on-demand resources and services (AWS, Azure, Google Cloud)
  • Cloud services include Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS)
• Content Delivery Networks (CDNs) distribute content to geographically dispersed servers, improving performance and availability (Akamai, Cloudflare)
• Network virtualization creates logical, software-based networks that are decoupled from the underlying physical infrastructure
  • Virtual LANs (VLANs) partition a physical network into multiple logical subnetworks, enhancing security and flexibility
• Software-Defined Networking (SDN) separates the control plane from the data plane, enabling centralized, programmable network management (OpenFlow)
• Wireless sensor networks consist of spatially distributed autonomous sensors that monitor physical or environmental conditions (temperature, pressure, motion)
• Peer-to-peer (P2P) networks allow nodes to act as both clients and servers, sharing resources and workload without a central authority (BitTorrent, Blockchain)